1. Field of the Invention
This invention relates to a magnetic recording medium, a magnetic head and a magnetic recording apparatus. More particularly, the present invention relates to a carbon protective film used on a sliding surface of a magnetic recording medium on a magnetic head in a magnetic dick apparatus, a floppy disk apparatus, a magnetic tape apparatus, and so forth.
2. Description of the Related Art
Recently, higher recording densities and greater capacities have been required for magnetic disk device. To promote these higher densities and capacities, the performance of the head and the medium must be improved and the floating gap between the head and the medium reduced. As a matter of fact, manufacturers have attempted to use a novel magneto-resistive head to the head/medium system and a novel head/medium system for vertical recording. On the other hand, the floating distance between the head and the medium has been reduced to about 0.1 .mu.m.
With the recent demands for greater capacity in a magnetic disk apparatus and for smaller size, a magnetic head utilizing an MR device (or an MR head) has been developed. To allow a current to flow directly through the device, the MR head needs an insulating protective film on its sliding surface. As to a protective film on the magnetic disk, a protective film having excellent insulating property is similarly required.
Further, because an improvement in the reliability of the magnetic disk apparatus was required, magnetic disks and a magnetic heads which are highly resistant to head crushes and have high durability are required, and a protective film having high hardness, such as a hydrogen-containing carbon film, has now been developed.
FIG. 28 is a plan view showing the internal structure of a magnetic disk apparatus. While a magnetic disk M is rotating at a high speed, a magnetic head h moves in a substantially radial direction to execute a seek operation, and recording/reproduction of information can then be carried out.
FIG. 29 is an enlarged sectional view of the magnetic disk M cut at the position of the magnetic head h and enlarged. In the thin film type magnetic disk M, reference numeral 1 denotes a substrate made of a non-magnetic substance such as aluminum or glass. While a NiP plating layer 2 is formed on the surface of the substrate so as to improve a mechanical strength, a Cr foundation layer 3 is formed to a film thickness of about 1,000 .ANG. by sputtering so as to improve horizontal orientation of the Co alloy.
After a thin film magnetic film 4 is formed by sputtering a magnetic material such as CoCrTa or CoNiCr to a thickness of about 500 .ANG., carbon is sputtered to a thickness of about 300 .ANG. as a protective film 5. Finally, a fluorine type lubrication layer 6 such as a perfluoropolyether is coated to some dozens of angstroms (.ANG.) and the product is completed.
When this magnetic disk M is rotated at a high speed in a direction represented by an arrow a.sub.1, the magnetic head slider 7 flies, at a very small height in an air stream flowing past an inflow slope S, so that recording and reproduction of information can be made to and from the magnetic film 4 of the magnetic disk by the electromagnetic conversion device 8 which is in a non-sliding condition.
The slider 7 of the magnetic head is fitted to a spring arm 11 through a gimbal 10, and a seek operation is carried out by a driving arm 13 on a carriage 12. Due to the simplicity of the mechanism as described above, a CSS (Contact Start Stop) system, wherein a core slider slides on the lubrication layer 6 at the starting and stopping of the apparatus, has been widely used.
FIGS. 30A to 30F are sectional views showing, step-wise, a production method for a thin film type magnetic disk according to the prior art, and this method is also described in Japanese Patent Application No. 3-336459 previously filed by the Applicant of the present invention. At the step shown in FIG. 30A, reference numeral 1 denotes a doughnut-like substrate made of a non-magnetic substance such as aluminum. This substrate is shaped into the same size as that of the magnetic disk which is to be fabricated. When a small diameter magnetic disk of 2.5 in. is to be produced, for example, a non-magnetic disk 1 having a diameter of 2.5 in. is used.
At the step shown in FIG. 30B, a NiP plating foundation layer 2 is formed on both surfaces of the non-magnetic disk 1, and fine texture grooves 8 are formed in a circumferential direction by pushing an abrasive tape to the sheet surfaces of the rotating non-magnetic substrate as shown in FIG. 30C.
At the next step shown in FIG. 30D, a Cr foundation layer 3 is formed, to a thickness of about 1,000 .ANG., on the texture groove 8 so as to improve the horizontal orientation of the Co alloy, and a magnetic film 4, consisting of a Co alloy, for example, is formed to a thickness of about 500 .ANG. on the Cr foundation layer 3 as shown in FIG. 30E. A hydrogen-containing carbon film 5 is formed, as a protective film, to a thickness of about 300 .ANG. on the magnetic film 4 as shown in FIG. 30F, and finally, a fluorine type lubrication layer 6 is coated on the carbon film 5. The Cr layer 3, the thin film type magnetic film 4 and the carbon film 5 are formed by a thin film formation technology such as sputtering.
The texture groove 8 formed at the step shown in FIG. 30C is formed in order to provide magnetic anisotropy so that electromagnetic conversion characteristics can be improved at the time of recording and reproduction of information.
Because the carbon film 5, too, is affected by the texture groove 8, the lubricant can prevent the magnetic head from being adsorbed to the magnetic disk surface, and the friction between the magnetic head and the magnetic head surface can be reduced.
As the floating distance between the head and the medium has been reduced in recent types of heads, the probability that the head comes into contact with the medium has increased. Accordingly, in order to produce such a head and a medium, development of a protection and lubrication treatment which is more durable has become indispensable.
To improve the durability of the treatment, various methods have been proposed in the past, such as a method which forms an amorphous carbon film by sputtering, a method which introduces hydrogen into a carbon film and converts the film structure to a diamond-like structure so as to improve mechanical characteristics by improving a film hardness and impact resistance, a method which applies a perfluoropolyether having a functional group with a foundation layer, as a lubricant, and so forth, and some of these methods have already been put into practical use.
As described above, it has been confirmed that the application of the hydrogen-containing film is effective for improving the mechanical characteristics. As a result of intensive studies, however, the inventors of the present invention have found out that when a hydrogen content exceeding a specific quantity is used, the adhesion strength with the lubricant drops. The drop in the adhesion strength between the protective film and the lubricant invites problems in the CSS (Contact Start Stop) system and in a high-speed magnetic disk apparatus in that film decrease of the lubrication layer becomes remarkable, and that the durability as well as the reliability drop.
The magnetic head shown in FIG. 29 is of a monolithic type, whereas the head shown in FIG. 13 is thin film magnetic head. A head device portion 14 is formed, using a thin film technique, and is covered with a protective film such as Al.sub.2 O.sub.3. A slider 7 has float rails 15, 16 on both sides of the slide surface, and inflow slopes 15s, 16s, for taking in an air stream, are defined on the opposite side to the head device portion 14.
FIGS. 14, 15A and 15B are schematic views useful for explaining a method of mass-producing the thin film magnetic head typically illustrated in FIG. 13. FIG. 14 shows a method of forming a large number of head device portions in a matrix form on a substrate, and FIGS. 15A and 15B illustrate a method which separates and finishes, one by one, the slides from a line in a slider block.
As shown in FIG. 14, a large number of head device portions 14 are first formed on a substrate 7W made of ferrite or Al.sub.2 O.sub.3 Tic by thin film technology, and are then separated, one by one, from the positions by cut lines 18, 19. In this way, the thin film magnetic head shown in FIG. 13 can be completed. In the production sequence, however, the device portions are first cut and separated at the position of the cut line 18 in the transverse direction, and a core slider block 20 having head device portions 14 aligned in a line is formed.
The slider blocks 20 thus separated are ground and machined, one by one, so as to form the float rails 15, 16 as shown in FIG. 15A. In other words, a groove 21 between the right and left float rails 15, 16, and a groove 22 between the adjacent sliders are formed. Next, while the core sliders are cut and separated, one by one, at the position of the cut line 19 at the center of the groove 22, they are bonded to a jig 23, with a predetermined gap, as shown in FIG. 15B, and are slid, by pushing them, to a lapping tape 25 bonded to a rubber stool 24 in such a manner as to grind the peripheral edges of the float rails 15, 16 and to conduct R chamfering. After R chamfering, the sliders are peeled from the jig 23, and are bonded and fixed one by one to gimbals 10 at the distal end of spring arms 11 as shown in FIG. 10. Then, while the slider 7 floats at a very small distance G, due to the circulated air caused by the revolution of the magnetic disk D, above the disk D recording and reproduction of information can be carried out.
In the CSS system apparatus, the force due to the circulated air does not instantaneously occur at the time of start and stop of the magnetic disk until the circulating air achieves a critical velocity. Consequently, the slider slides on the lubrication layer 6 of the magnetic disk. Because of this, wear gradually proceeds on both the lubrication layer 6 and the core slider 7 and, in the worst case, information in the magnetic film 4 of the magnetic disk can be lost.
To prevent such a problem, a carbon-type protective film 5 is formed on the magnetic disk surface and a layer 6 of the lubricant is further formed on the carbon-type protective film 5 as shown in FIG. 29, so as to reduce wear of the magnetic disk surface. However, as minaturization of the magnetic disk apparatus has proceeded, CSS frequency is by far higher in a compact apparatus in which frequency of start/stop of the magnetic disk increases, than in a large-scale apparatus. Accordingly, counter-measures against wear have become more important.
When the wear of the magnetic disk surface proceeds and dust due to wear increases in the magnetic disk apparatus, the dust mixes with the lubricant on the magnetic disk surface and changes to debris. In other words, the dust of wear gathers together due to viscosity of the lubricant and grows to a lump. The debris, is clay-like and adheres to the slider 7 as represented by reference numeral 26 shown in FIG. 29, and upsets the balance of the slider. Therefore, stable floating becomes difficult, and the head is likely to impinge against the magnetic disk surface and to cause a head crash. When the debris adheres to the inflow slopes 15s and 16s as shown in FIG. 13, the floating distance decreases, and the head is likely to come into contact with the magnetic disk surface.
When the debris adheres to the magnetic disk surface, and the magnetic disk surface comes into contact with the slider during the CSS operation, the load to the motor becomes excessively large at the start. Accordingly, the magnetic disk is unable to rotate, or it impinges against the magnetic disk surface due to the reaction when the slider is freed from the magnetic disk surface, on a head crash occurs, or the magnetic disk surface is damaged.
On the other hand, a magnetoresistive type magnetic head (MR head) has been developed to satisfy the requirements for greater capacity and a smaller size in the magnetic disk apparatus. In the case of this MR head, the MR device is formed at the head device portion 14 shown in FIG. 13.
In the case of an apparatus wherein the magnetic head is very likely to come into contact with the magnetic disk due to the low flying height of the magnetic head or in the case of a floppy disk apparatus using the MR head or in the case of a magnetic tape apparatus or an apparatus wherein frequency of sliding is high or sliding always takes place, a head crash must be prevented and durability must be improved. However, the conventional carbon film does not have sufficient wear resistance.
Therefore, a thick protective film having thickness in the range of from about 300 .ANG. to about 400 .ANG. becomes necessary, but when the film becomes thick, the distance between the electromagnetic conversion device and the recording layer increases and recording and reproduction characteristics deteriorate. For this reason, the thickness of the protective film must be reduced to about 100 to about 200 .ANG.. Further, because the conventional carbon protective film has a low insulating property, the current directly applied to the MR device is likely to leak to the magnetic disk, etc.